Self-crimping, self-bonding fibrous polyolefin tobacco smoke filter



y 23, 1968 R. c. MUMPOWER u, ETAL 3,393,685

SELF-CRIMPING, SELF-BONDING FIBROUS POLYOLEF'IN TOBACCO SMOKE FILTER Filed Oct 24. 1965 m m r CIGARETTE PAPER FILTER WRAPPER ROBERT c- MUMPOWER 1 JOHN w- TAMBLYN mvsmons SELF BONDING AND SELF- CRIMPING F IL TE R ATTORNEYS United States Patent 3,393,685 SELF-CRIMPING, SELF-BONDING FIBROUS POLYOLEFIN TOBACCO SMOKE FILTER Robert C. Mumpower II, and John W. Tamblyn, Kingsport, Tenn., assignors to Eastman Kodak Company,

Rochester, N.Y., a corporation of New Jersey Filed Oct. 24, 1965, Ser. No. 504,462 Claims. (Cl. 131-267) ABSTRACT OF THE DISCLOSURE A self-bonding and self-crimping cigarette filter made from two or more synthetic filaments, one of which has a lower melting point and one of which has greater shrink-age when subjected to heat. The filament of lower melting point acts to bind together the filaments when subjected to heat. The filament of greater shrinkage acts to randomly crimp the filaments which are bonded to it when subjected to heat.

This invention relates in general to tobacco smoke filters formed from a mixture of synthetic fibers. More particularly, the invention relates to cigarette filters made from a fibrous filter tow composed of two or more types of fibers, one of which can be heat-shrunk much more than the rest and at the same time softened enough to stick to the non-shrinking fibers.

Over the past decade a wide variety of materials have been tested and recommended as good filter media for tobacco smoke. Cotton wads, creped tissue paper and regenerated cellulose fibers were among the first of these materials to actually be tried on a commercial basis as a lter media for such tobacco products as cigarettes. Although filters made from these natural fiber materials did remove certain amounts of the deleterious constituents found in tobacco smoke they nevertheless failed to find wide acceptance in the trade because of certain inherent disadvantages characteristic of these types of materials. For example, filters made from paper, cotton, regenerated cellulose fibers or the like become soft and soggy when tobacco smoke passes through them. Furthermore, these filters produce an objectionable taste that greatly detracts from the quality of the smoke.

The shortcomings of these early tobacco smoke filters made from natural occurring materials led to the investigation of synthetic fibers as tobacco smoke filter media. Out of the numerous kinds of synthetic fibers tested and evaluated, cellulose acetate has been found to possess certain desirable attributes and thus has gained rather widespread acceptance within the trade. As is well known, cellulose acetate or other like organic solvent synthetic fibers from which tobacco smoke filters are made is formed by a spinning or extruding process. In substantially all spinning processes heretofore known or practiced in producing such filter fibers the fine streams of spinning solution immediately upon leaving spinnerette orifices, and before any substantial solidification has taken place, are subjected to a certain amount of tension which is normally imposed by a positive drawing of the filaments from the spinnerette. This tension causes substantial elongation of the fine streams of spinning solution before and during transformation into self-sustaining filaments. The imposed tension and the internal strain set up in the filamentous structures at the time of their birth bring about substantial orientation of the molecules along the filament or fiber axis. The formed filaments are, therefore, inherently straight and can be drawn or otherwise arranged in a substantially parallel relationship to form a tow which is adaptable for use in the manufacture of cigarette filter elements.

However, as is well known in the tobacco smoke filter 3,393,685 Patented July 23, 1968 art, the parallel fibers from which the filter is to be formed must be crinkled or crimped if the best possible filtering action is to be obtained. Thus it has always been necessary to subject the substantially straight filaments or fibers of the filter tow to any of several after-treatments to .produce the desired c-rimps. For instance, the crirnps may. be produced mechanically by means of intermeshing gear-like elements, by means of a stuffer box type crinkler, or by twisting the fibers, setting the twist and then untwisting.

As will be apparent, not only does this additional step Ofcrimping otherwise parallel fibers require a separate processing step which is both time consuming and expensive, but the crimped tow must be handled very carefully during shipment and formation of the filter elements or the fibers will be stretched and the crimps thus removed. This special handling problem, therefore, also represents a very decisive disadvantage in using such crimped tow materials in manufacturing tobacco smoke filters.

Furthermore, the synthetic fibers from which the cigarette or like tobacco smoke filter element is to be made must be bonded together to form a rigid filter. In the case of cellulose acetate fiber tow this bonding can be obtained through the use of a non-volatile liquid organic plasticizer which is applied to the tow just prior to its being formed into a filter rod. This plasticizer, which is normally sprayed on the tow as fine droplets, gradually dissolves those points on the fibers which it touches making an adhesive area capable of bonding adjacent fibers in the tow in a random manner. This random fusing of the fibers at various points throughout the filter produces the proper rigidity needed to cut the rod into filter tips. Even though such an operation which employs a non-tacky type of bonding agent that bonds the fibers gradually after they are in the form of a filter has obvious advantages over the application of conventional adhesives that produce a tacky surface on the tow immediately after their application and thus causes the tow to adhere to the various parts of the machinery during the fabrication of the filter rod, it still leaves something to be desired. For example, the application of the plasticizer requires special equipment and an additional processing step. Furthermore, such plasticizers have been known to impart an objectionable taste to the tobacco smoke and may also mask certain filter additives such as activated carbon thereby reducing their effectiveness unless special precautions are taken.

Another disadvantage of using a filter tow made from crimped fibers is that the tow must be bloomed" or fluffed out prior to the fabrication of the filter rod. This blooming operation is a mechanical treatment well-known in the art of cigarette filter manufacture in which the individual fibers of the tow are opened or flufied in such a manner as to partially deparallelize the individual filaments and give the tow increased bulk. The first step in this operation is to pass the filter tow, as it comes off the bale or other package, through a special device known as a banding jet which causes the rope or bundle of crimped filamentary material to become flattened out into the form of a band or ribbon as it is conveyed through the device by a blast of air. The band of filaments thus produced is then passed through a set of pretensioning rolls which serve to debundlize the filamentary material, that is, to separate the individual fibers one from another, partially deparallelize them and give the band increased bulk. The crimped filter tow is now ready for the plasticizer to be added after which it is gathered and compressed into a filter rod.

From the foregoing it is readily apparent that the production of a filter rod having the numerous advantages of a crimped cellulose acetate filter rod, but without any of its disadvantages would represent a very desirable and long searched for advancement in the art of manufacturing tobacco smoke filters. According to this invention it has been found that such a new and novel filter rod can be produced by blending together two or more different types of fibers, one of which softens and shrinks at a low temperature, and then heating the filter rod formed from the blend. This heating causes the low thermoresponsive fibers to soften and become randomly attached to the other fibers of the filter after which the softened fibers shrink thereby crimping the attached fibers. Thus a self-bonding and selfcrimping action occurs within the filter rod after it has been formed.

Therefore an object of this invention is to produce a selfbonding and self-crimping tobacco smoke filter.

Another object of this invention is to produce a selfbonding and self-crimping tobacco smoke filter made from a blend of two or more fibers, one of which softens and shrinks to a large degree when subjected to heat.

Yet another object of this invention is to produce an internally bonded and crimped filter rod made from a blend of drafted and undrafted thermoresponsive fibers.

A special object of this invention is to provide a self bonding and self-crimping cigarette filter made from a blend of undrafted polypropylene and highly drafted polyethylene fibers.

These and further objects and advantages of this invention will be more apparent upon reference to the following description, specific working examples, appended claims and drawings wherein:

FIGURE 1 is a diagrammatic view showing the various stages involved in the preparation of a self-bonding and self-crimping filter element of the present invention, as well as the apparatus required;

FIGURE 2 is a greatly magnified view of a plurality of self-bonded an'd self-crimped fibers within a filter rod produced in accordance with this invention prior to their be- Ing subjected to heat;

FIGURE 3 is a view of the fibers in FIGURE 2 after heat has been applied to the filter rod; and

FIGURE 4 is a perspective view, with portions thereof cut away, of a cigarette with a filter made in accordance with this invention.

With continued reference to the accompanying figures wherein like reference numerals designate similar parts throughout the various views, and with initial attention directed to FIGURE 1, reference numeral is used to generally designate a filter forming apparatus constructed in accordance with the concepts of the present invention. As mentioned hereinabove, the filter tow 12 is formed from two or more fibers, one of which has a lower softening temperature and a higher shrinkage value than the other. For purposes of illustration this blend of fibers is shown being furnished from a plurality of reels or drums 14 and 16, although it should be realized that various other methods of furnishing the blended tow are available and can be readily adapted to the present invention. Preferably the tow 12 consists of undrafted fibers 18, such as polypropylene, blended with highly drafted fibers of the polyethylene class. The ratio of the undrafted to drafted fibers in the filter tow 12 may range from 10 to 90 percent by weight and can easily be adjusted simply by varying the ratio of the various reels furnishing the fibers for the tow. However, the preferred blend contains 50 percent by weight of the low melting, highly drafted polyethylene class fiber 20.

Upon leaving the reels 14-16 the undrafted and drafted fibers 1820 pass through a trumpet or cone 22 where they are gathered and compressed into a cylindrical shaped rope 24. Since no adhesive or plasticizer type bonding agent is to be applied to the filter tow 12, the individual fibers need not be bloomed out or otherwise modified prior to their entering the trumpet 22. If necessary or desirable a paper wrapper can be placed around the filter rope 24 in a conventional manner at the time it is being formed or at some suitable time thereafter. A cutter block 4 26 and knife blade 28 are provided for cutting the filter rope 24 as it emerges from the trumpet 22 into proper length filter rods 30. The filter rods 30 cut from the rope are placed in a suitable oven 32 which for purposes of illustration is shown as a metal box 34 surrounded by an insulative layer 36 that has a heating element 38 embedded therein. Obviously any other suitable heating device can be used in place of, or in conjunction with, the oven 32.

As shown in FIGURE 2 the undrafted polypropylene fibers 18 within the filter rod 30 have a rather rough outer surface due in part to the fact that they are undrafted, but are otherwise substantially straight. The polyethylene fibers 20 are somewhat more uniform in appearance than the undrafted fibers 18 and, due to their having been highly drafted, are nearly perfectly straight. As is to be expected, the various fibers within the compressed filter rod 30 touch one another at random points such as shown at 40'.

When heat is applied to the filter rod 30 by the oven 32 or other like heating element, two separate but interrelated events occur. First, the fiber with the lowest softening point, which in this case is the highly drafted polyethylene fibers 20, will become soft and adhere to the other fibers, and to one another, at their various random points of contact. This effectively results in all the individual fibers within and making up the filter rod 30 being bonded together into a unitary mass. Secondly, the applied heat will cause one group of fibers from which the filter rod 30 is made to shrink. Again, the polyethylene fibers will be the ones to shrink in the present instance due to their having been highly drafted. After the bonding and shrinkage of the fibers have occurred the filter rods are cooled and cut into suitable filter elements. FIGURE 3 illustrates how the shrinkage of the highly drafted polyethylene fibers 20 will result in random crimps being formed in the bonded together fibers and especially the fibers 18. These crimps are very irregular in amplitude and extend in three dimensions as distinct from mecanically imposed crimps produced heretofore which lie in but one plane and require no continuous constrictive force for their existence. Thus, the reduction in length of the filter element 30 from a preheated length 1 (FIGURE 2) to a length I after heating, or a distance of x, produces such a constrictive force that crimping or buckling of the fibers is induced to such an extent as to substantially block all channels that would otherwise extend straight through the filter elements. This results in rather meandering or random passageways being provided through the filter which the efiiuent stream of tobacco smoke will have to follow in reaching the smoker.

A further understanding of the invention will be had from a consideration of the following examples that may be used in actual commercial practice and are set forth to illustrate certain preferred embodiments.

EXAMPLE 1 A 50-50 blend by weight of 3 denier/filament (D/ F undrafted polypropylene and 3 D/F low density polyethylene fiber which had been drafted were blended into a tow of 120,000 total denier. The uncrimped and loose two was placed in an 8 mm. inside diameter (I.D.) glass tubing and heated to C. for 20 minutes. The tow shrank in length by 30 percent and the fibers were found upon inspection to be highly crimped and buckled and bonded together at random spots by the melting and shrinkage of the polyethylene fibers. The self-crimped and self-bonded materials were then removed from the glass tube, wrapped in cigarette paper, and cut into cigarette filter lengths (17 mm.) with a razor blade. The filters were then attached to king-size commercial cigarettes that had been shortened by 17 mm. to compensate for the added filter tip. The filter cigarettes were then smoked on an. analytical-type machine as described in Tobacco Science, 5, p. 31, l96l and were found to remove 24 percent of the solid constituents in the tobacco smoke at a pressure drop of 3.9 inches of water (as measured with an air flow of 17.5 nil/second).

EXAMPLE 2 A blend of 70 percent by weight of 4 D/F polypropylene fibers and 30 percent by weight of 5 D/F fibers from a vinyl acetate and ethylene copolymcr were placed in an 8 mm. ID. glass tube. The uncrimped and loose filter tow was then heated for one hour at 80 C. The tow shrank in length by about 25 percent and was bonded by the melting of the acetate fibers into a firm but porous structure. The self-bonded and self-crimped filter rod was removed from the glass tube, wrapped in cigarette paper and cut into 17 mm. cigarette filter tips. The filters were then evaluated in the same manner as described in Example 1 and found to remove 25 percent smoke solids at a filter pressure drop of 2.6 inches.

EXAMPLE 3 A 67-33 percent by weight blend of 4 D/F cellulose acetate fibers and 8 D/ F polypropylene fibers was made into a filter tow of 60,000 total denier. The tow was then converted to 90 mm. filter rods that were wrapped in cigarette papers. The uncrimped filter rods were then heated in an oven for 30 minutes at 160 C. The rods were found to be firm and had shrunk in length by percent. The filter rods were cut into 17- mm. filter tips which were evaluated in the same manner as described in Example 1 and found to remove 27 percent smoke solids at a filter pressure drop of 2.5 inches.

From the foregoing it is readily seen that a cigarette filter produced from a structure of self-crimping (or bulking) and bonding polyolefin fibers completely eliminates such problems as softness, sogginess and objectionable taste that have heretofore been found to exist in known commercial tobacco smoke filters. Furthermore, the selfbonding and self-crin1ping filters eliminates many of the processing steps and much of the expensive manufacturing equipment that was heretofore thought to be necessary to produce tobacco smoke filters. The elimination of these process steps and equipment tends to increase the speed at which filter rods can be produced while lowering their total production costs.

As brought out by the above examples, various types, sizes and percentages of fibers can be blended to produce superior filter elements so long as one of the fibers will soften thereby bonding the filter together, and the fibers of the filter are then buckled or crimped through the shrinkage of a fiber group incorporated into the bonded filter. Numerous combinations of fibers can be produced which will give this desired two-fold action. For example, the two active fibers from which the filter is constructed could be: (1) high-density (high-melting) polyethylene and low-density (low-melting) polyethylene; (2) poly-4- methyl pentene-1 (high-melting) and polyethylene (lowmelting); poly-3-methyl-butene-l (high-melting) and polypropylene (low-melting); or elastomeric ethylenepropylene terpolymers could be used for one of the component fibers. Furthermore, polyethylene cross-linked by ionizing radiation or other known means could be used, if desirable, as a method of increasing the degree of shrink obtainable.

As will be apparent, the amount of draft (if such is required), time of heating, and temperature to be employed will vary over a wide range depending on the type of fibers that are blended together to form the tobacco smoke filter. In any event, the draft should be high enough to cause the desired filter shrinkage and fiber buckling to occur when the drafted fiber is heated. The temperature as well as the time range must be sufficient to permit the low-melting fibers of the blend to soften and adhere the fibers together in addition to causing the selected crimp producing fibers to shrink. Under certain conditions it may be desirable to use a filter tow made from a blend of fibers in which one group of fibers will soften to bond the filter together while a second group of fibers will cause the desired fiber crimping or filter shrinkage to occur when heated.

What is claimed and desired to be secured by the United States Letters Patent is:

1. An article of manufacture comprising a porous filter element adapted for clarifying an efiluent stream of tobacco smoke, said element comprising a blend of bonded together and self-crimped filaments of at least two types of synthetic filaments, one type of said filaments having a higher thermal shrinkage value than the other type of filament, at least part of said bonded filaments of lower shrinkage value having been buckled and crimped by shrinkage of said filaments of higher shrinkage value after said bond had been effected, said filter element having continuous passages that meander therethrough.

2. An article of manufacture comprising a porous filter element adapted for clarifying an effluent stream of tobacco smoke, said element comprising a blend of bonded together and self-crimped synthetic filaments of at least two types, one type of said fibers having a lower melting point than the other type of said fibers, one type of said fibers also having a higher thermal shrinkage than the other type of said fibers, said bonded filaments of higher thermal shrinkage value having been shrunk, with at least part of said bonded filaments of lower thermal shrinkage value having been buckled and crimped by shrinkage of the high shrinkage filaments after said bond has been effected, said filter element having passages that meander therethrough.

3. An article of manufacture comprising a porous filter element according to claim 2 wherein both said high 3nd low melting point filaments are made of polyole- 4. An article of manufacture comprising a porous filter element according to claim 3 wherein said filaments of higher melting point are made of polypropylene, and said filaments of lower melting point are made of polyethylene.

5. An article of manufacture comprising a porous filter element according to claim 4 wherein said polypropylene filaments are undrafted, and said polyethylene filaments are drafted.

6. An article of manufacture comprising a fibrous filter element for clarifying an effluent stream of tobacco smoke, said element comprising a blend of at least two types of synthetic filaments extending longitudinally along said element, one type of said filaments having a melting point lower than that of the other type of filaments, one type of said filaments also having a greater shrinkage than that of the other type of said filaments, the filaments of the two types being mixed for substantially uniform distribution of the filaments of one type among the filaments of the other type, the filaments of lower melting point being bonded to the filaments of the higher melting point by softening of said filaments of lower melting point while said filaments of higher melting point are unsoftened and by cooling of said element, said bonded filaments of the higher shrinkage being shrunk, said bonded filaments of the lower shrinkage being buckled and crimped by shrinkage of said bonded filaments of the greater shrinkage, said filter element having passages that meander therethrough and along which the efiiuent stream of smoke passes.

7. An article of manufacture comprising a fibrous filter element according to claim 6 wherein said element consists essentially of undrafted polypropylene filaments and of highly drafted polyethylene filaments, and wherein the polyethylene filaments have both the lowest melting point and the greatest shrinkage.

8. An article of manufacture comprising a fibrous filter element according to claim 7 wherein the polyethylene filaments constitute from 10 to percent by weight of said element.

9. An article of manufacture comprising a fibrous filter element according to claim 8 wherein the polyethylene filaments constitute approximately 50 percent by weight of said element.

10. An article of manufacture comprising a fibrous filter element according to claim 6 wherein the two types of filaments are selected from the group consisting of: (1) high-density polyethylene filaments and low-density polyethylene filaments; (2) poly-4-1nethyl pentene-l filaments and polyethylene filaments; (3) poly 3-methy1 butene-l filaments and polypropylene filaments; (4) polypropylene filaments and vinyl acetate-ethylene copolymer filaments; and (5) cellulose acetate filaments and polypropylene filaments.

References Cited UNITED STATES PATENTS SAMUEL KOREN, Primary Examiner. m D. J. DONOHUE, Assistant Examiner. 

